Liquid Breathing, the process of ventilating the lungs with an oxygenated liquid is believed to have important medical applications. Development of a system enabling liquid respiration to be performed is of prime importance in its application. When a liquid replaces gas as the medium in which oxygen and carbon dioxide are transported, several problems not typical in gas respiration develop. The increased mass and viscosity of a liquid as compared with a gas require some means of mechanical assistance. The lower diffusion rates of gases in liquids as compared with gas rates places limitations on the design of a mechanically assisted liquid breathing system. Serial lung lavage has been reported in successful treatment of alveolar proteinosis, status asthmaticus, chronic bronchitis and cystic fibrosis. During serial lung lavage one lung is maintained on oxygen while the other is lavaged. The present study is directed toward developing a system which will permit lavage of both lungs simultaneously (parallel). The liquid breathing circuit consists of the following elements: 1. electrically operated, linearly actuated, bellow pumps. 2. liquid regenerator with heater and temperature controller. 3. oxygen source. 4. electronic controller. 5. solenoid and check valves. 6. pressure and temperature transducers. 7. flow control valves. 8. function generator for controlled respiration. Current objectives include evaluation of impact of the liquid breathing system on the biological system and reduction of the system to a clinical device for use in parallel lung lavage. Analytical models have been formulated for the dynamics of lung-mechanical system interactions and aid in the design, construction and testing of liquid breathing systems and components.